Carmine is a red pigment made from dried cochineal, a scale insect that has been a source of brilliant scarlet reds in clothing and art for more than two millennia, with records dating back to 700 BC. Since the 16th century, it has been intensely traded all over the world and was one of the most important trade goods for the Spanish empire at its economic peak. Despite still being used on an industrial scale, with hundreds of metric tonnes produced annually, the exact molecular and crystal structures of the dyestuff remains undetermined. Notably, both modern-day commercial carmine and pigments prepared following historical recipes show strikingly similar diffraction patterns, indicating a common crystalline structure. Here we show that the crystal structure of carmine can, at last, be determined using three-dimensional electron diffraction measurements, revealing a tetranuclear complex that assembles into a nanoporous supramolecular structure with pore diameters of approximately 1.8 nm, held together by intermolecular hydrogen bonding. Our results establish a definite structure of carmine, unveiling a surprisingly complicated arrangement in a long-used commodity with economic and cultural impact, while also highlighting the serendipitous creation of a man-made supramolecular material that dates back hundreds if not thousands of years.

The V-shaped linker molecule 2,5-furandicarboxylic acid (H₂FDC), which can be derived from lignocellulosic biomass, was used in a systematic screening with various iron salts and led to the discovery of a new iron-based metal–organic framework (Fe-MOF) with the composition [Fe₃(μ₃-O)(FDC)₃(OH)(H₂O)₂]·5H₂O·H₂FDC, designated as CAU-52 (CAU = Christian-Albrechts-Universität zu Kiel). The crystal structure of CAU-52 was determined using 3D electron diffraction (3D ED) and further refined by Rietveld refinement against powder X-ray diffraction (PXRD) data. CAU-52 contains the well-known trinuclear [Fe₃(μ₃-O)]⁷⁺ cluster as the inorganic building unit (IBU) that is six-connected by FDC^2– ions to form the pcu net. The connectivity leads to two types of cubic cages, similar to the ones observed in soc-MOFs. Comprehensive characterization of the title compound, including N₂ and water vapor sorption measurements, confirmed its chemical composition. CAU-52 exhibits microporosity toward nitrogen with a type-I isotherm (77 K), yielding a specific surface area of a_s,BET = 1077 m²/g. The H₂O sorption measurement at 298 K leads to an isotherm that exhibits three steps. The water sorption capacity was determined to be 390 mg/g, and it decreases slightly in subsequent sorption cycles. The MOF is stable up to 250 °C in air and chemically resistant in various solvents.

In the field of metal-organic frameworks, the use of yttrium(iii) cations and the formation of 3D inorganic building units are rather rare. Here we report an yttrium(iii) metal-organic framework based on the V-shaped ditopic linker 4,4′-oxydibenzoate, oba2−: [Y16(μ-OH2)(μ3-OH)8(oba)20(dmf)4]·7H2O·7dmf, 1, which was solvothermally prepared, with single crystal X-ray diffraction revealing an unusual 3D metal secondary building unit. When activated at 200 °C, 1 desolvated to form compound 2, [Y16(μ-OH2)(μ3-OH)8(oba)20]·6H2O, retaining the same structure with a 3% shrinkage in unit cell volume.

In this work, melem-based supramolecular assemblies were obtained in one step by thermal treatment of melamine in an autoclave in the presence of sodium chloride. The detailed analysis showed that the obtained powder consists of two phases: poorly crystalline Na-PHI flakes and rod-shaped melem hydrate single crystals (several micrometers long and ~300–500 nm wide). Melem hydrate crystals absorb light in the visible range (Eg=2.7 eV) and demonstrate photocatalytic activity in the reaction of partial oxidation of benzyl alcohol to benzaldehyde by air under visible light with high selectivity for the target product. At 60 % conversion of benzyl alcohol, the selectivity of benzaldehyde formation is above 95 %.

A family of responsive enaminitrile molecular switches showing tunable turn-on fluorescence upon switching and aggregation is reported. When activated by the addition of acid/base, isomerization around the C═C bond could be effectuated, resulting in complete and reversible switching to the E- or Z-isomers. Typical aggregation-induced emission (AIE) could be recorded for one specific state of the different switches. By subtle tailoring of the parent structure, a series of compounds with emissions covering almost the full visible color range were obtained. The switchable AIE features of the enaminitrile structures enabled their demonstration as solid-state chemosensors to detect acidic and basic vapors, where the emission displayed an “off-on-off” effect. Furthermore, switching to the Z-configuration could be driven out-of-equilibrium through transient changes in acidity while giving rise to fluorescence. Single-crystal X-ray diffraction measurements suggested a luminescence mechanism based on restriction of intramolecular rotation and an intramolecular charge transfer effect in the AIE luminogens.

Aluminum acetates have been in use for more than a century, but despite their widespread commercial applications, essential scientific knowledge of their synthesis-structure-property relationships is lacking. High-throughput screening, followed by fine tuning and extensive optimization of reaction conditions using Al3+, OH− and CH3COO− ions, has unraveled their complex synthetic chemistry, yielding for the first time the four phase pure products Al(OH)(O2CCH3)2 ⋅ x H2O (x=0, 2) (1A and CAU-65, 1B), Al3O(HO2CCH3)(O2CCH3)7 (2), and the porous aluminum salt [Al24(OH)56(CH3COO)12](OH)4 (CAU-55-OH, 3). Structure determination by electron and X-ray diffraction was carried out and the data suggested porosity for 1B and 3, which was confirmed by physisorption experiments. Even the scale-up to the 10 L scale was accomplished for 1A, 1B and 3 with yields of up to 1.1 kg (99 %). This study of a seemingly simple chemical system provides important information on both fundamental inorganic chemistry and porous materials.

Zeolitic imidazolate frameworks (ZIFs) are a subclass of metal–organic framework that have attracted considerable attention as potential functional materials due to their high chemical stability and ease of synthesis. ZIFs are usually composed of zinc ions coordinated with imidazole linkers, with some other transition metals, such as Cu(II) and Co(II), also showing potential as ZIF-forming cations. Despite the importance of nickel in catalysis, no Ni-based ZIF with permanent porosity is yet reported. It is found that the presence and arrangement of the carbonyl functional groups on the imidazole linker play a crucial role in completing the preferred octahedral coordination of nickel, revealing a promising platform for the rational design of Ni-based ZIFs for a wide range of catalytic applications. Herein, the synthesis of the first Ni-based ZIFs is reported and their high potential as heterogeneous catalysts for Suzuki–Miyaura cross-coupling C─C bond forming reactions is demonstrated.

Alkali metal imidazolates are important compounds, serving as intermediates in organic synthesis and additives in alkali ion electrolytes. However, their solid-state structures and thermal behaviors remain largely unexplored. In this study, we present the synthesis, structural analysis, and thermal characterization of lithium and sodium benzimidazolate (bim-). The crystal structures of these microcrystalline materials, determined by 3D electron diffraction, reveal closely related layered coordination networks. In these structures, 4-fold N-coordinated alkali ions are bridged in two dimensions by bim- linkers, with the networks’ surfaces decorated by the phenyl rings of the bim- linkers, stacking atop one another in the solid state. Differential scanning calorimetry combined with variable temperature X-ray powder diffraction indicates that both materials melt above 450 °C. Additionally, Na(bim) undergoes a displacive phase transition from an ordered α-phase to a highly disordered β-phase before melting. Structural variations, primarily attributable to the differing ionic radii of Li+ and Na+, result in distinct coordination environments of the alkali metal ions and varying orientations of the bim- linkers. These differences lead to markedly distinct thermal behaviors: Li(bim) exhibits positive thermal expansion along all crystal axes, whereas Na(bim) switches from area negative thermal expansion (NTE) to linear NTE during the α → β phase transition.

The SARS-CoV-2 (COVID-19) pandemic outbreak led to enormous social and economic repercussions worldwide, felt even to this date, making the design of new therapies to combat fast-spreading viruses an imperative task. In the face of this, diverse cutting-edge nanotechnologies have risen as promising tools to treat infectious diseases such as COVID-19, as well as challenging illnesses such as cancer and diabetes. Aside from these applications, nanoscale metal-organic frameworks (nanoMOFs) have attracted much attention as novel efficient drug delivery systems for diverse pathologies. However, their potential as anti-COVID-19 therapeutic agents has not been investigated. Herein, we propose a pioneering anti-COVID MOF approach by studying their potential as safe and intrinsically antiviral agents through screening various nanoMOF. The iron(III)-trimesate MIL-100 showed a noteworthy antiviral effect against SARS-CoV-2 at the micromolar range, ensuring a high biocompatibility profile (90% of viability) in a real infected human cellular scenario. This research effectively paves the way toward novel antiviral therapies based on nanoMOFs, not only against SARS-CoV-2 but also against other challenging infectious and/or pulmonary diseases.

Sodium zirconate (sodium zirconium oxide; Na₂ZrO₃) is a widely investigated carbon dioxide (CO₂) sorbent. Since it was first discussed in the 1960s, Na₂ZrO₃ has been reported to adopt monoclinic, hexagonal, and cubic structures, and it is widely believed that the CO₂ capture performance of Na₂ZrO₃ is related to its crystal structure. Researchers have relied on the differences in the relative intensities of two peaks (2θ ∼16.2° and 38.7°) in the powder X-ray diffraction (PXRD) pattern to determine the phase of this compound. However, to date, a defined crystal structure of hexagonal Na₂ZrO₃ has remained elusive. Our findings show that the current literature discussion on the structure of Na₂ZrO₃ is misleading. With the use of 3D electron diffraction (3D ED), and PXRD, we prove that hexagonal Na₂ZrO₃ does not exist. The so-called hexagonal Na₂ZrO₃ is actually Na₂ZrO₃ with three different types of disorder. Furthermore, the two PXRD peaks (2θ ∼16.2° and 38.7°) cannot be used to distinguish the different phases of Na₂ZrO₃, as the change in the PXRD pattern is related to the extent of structure disorder. Finally, we also show that the CO₂ uptake properties of Na₂ZrO₃ are not related to the differences in crystal structures, but rather to the Na⁺ site occupancy differences in different Na₂ZrO₃ samples. In order to further develop applications of Na₂ZrO₃, as well as other mixed-metal oxides, their structures, and the existence of any disorder, need be understood using the methods shown in this study.